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* Texas Agricultural Experiment Station, Overton, TX 75684 and
and
University of Missouri-Columbia, MO 65211
4 Correspondence: P.O. Box 200 (phone: 903-834-6191; fax: 903-834-7140; E-mail:
r-randel{at}tamu.edu).
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Key Words: Bos indicus • Insulin-Like Growth Factor • Leptin • Reproduction
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Insulin-like growth factor-I and leptin are two hormones that may be involved in the effects of nutrition on reproduction. During periods of undernutrition, circulating concentrations of IGF-I and leptin decrease. Short-term fasting decreased circulating leptin and IGF-I concentrations and concurrently decreased the frequency of LH pulses (Amstalden et al., 2000). These data provide evidence of a potential association between IGF-I and leptin in the effects of nutrition on reproduction. Because ionophores improve feed efficiency and increase dietary energy and protein flow, provision of an ionophore might alter circulating concentrations of IGF-I and leptin. Ionophore supplementation to postpartum cows might also create differences between treated and untreated animals to allow a comparison of changes in IGF-I and leptin prior to return to estrus. This would further elucidate effects of these two hormones on reproductive performance. Therefore, objectives of this study were to determine effects of lasalocid ingestion on conception and pregnancy rates and serum concentrations of IGF-I and leptin, and whether these hormones were metabolic indicators of return to estrus in beef cows.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Cows were maintained together on Coastal bermudagrass pastures overseeded with ryegrass and were separated once daily for feeding. All cows were each fed an 11:1 corn:soybean meal supplement at 1.4 kg daily. In addition, the L cows each received 200 mg of lasalocid daily in the supplement. Treatments began 21 d prior to the predicted calving date. Thereafter, once weekly, any cows that were within 21 d of the predicted calving were added to treatment. Cows were weighed once every 2 wk and BCS was assessed. Approximately 10-mL blood samples were collected from cows once weekly before calving by caudal venipuncture. A blood sample was collected within 24 h of calving and blood samples were collected twice weekly (Monday and Thursday) after calving. Samples were refrigerated and subsequently centrifuged at 4°C at 3,000 rpm for 30 min. Serum was collected and frozen at -20°C until assayed for progesterone (P4), IGF-I, and leptin by RIA. Epididymectomized Bos taurus x Bos indicus bulls equipped with chinball marking harnesses were maintained with cows during the postpartum period for estrous detection. Eight days after cows were marked by the bull, and thus had shown signs of potential estrus, ovaries were evaluated by rectal palpation to determine whether a corpus luteum (CL) was present. Blood samples were collected on d 6, 7, and 8 following first estrus to confirm the presence of a CL by P4 concentrations. Once a cow had two ovulations with estrus and functional CL formation separated by a normal estrous cycle length (17 to 24 d; Senger, 1997), it was removed from the study.
At the start of the breeding season, cows that were removed from the study (L and C) were placed with a fertile Brahman bull equipped with a chinball marking harness to allow determination of first-service conception rate. The average cow was 70 d postcalving at this time. Due to the design of the study, some cows were removed from the study prior to the start of the breeding season. On average, however, cows were immediately placed with the bull. Of the two treatments, 6 L and 5 C cows were removed from treatment prior to the start of the breeding season, with the longest interval of removal being 21 d. Cows remained with the bull for the duration of the 60-d breeding season. Approximately 60 d after removal of the fertile bull, all cows were examined for pregnancy by rectal palpation.
All serum samples were analyzed for P4 concentration via RIA as described by Williams (1989). The antibody used was No. 337 anti-progesterone-11-BSA (G. D. Niswender, Colorado State University, Fort Collins, CO). The intra- and interassay CV for the P4 analysis were 9.4 and 10.2%, respectively. Progesterone concentrations greater than 1 ng/mL were considered to be indicative of a functional CL. Days to return to estrus were determined relative to estrus associated with the formation of a functional CL.
Weekly serum samples from the pre- and postpartum period were analyzed by RIA for IGF-I as described by Bilby et al. (1999), with the following modifications. Final antibody dilution was 1:120,000 and the goat-anti-rabbit antibody dilution was 1:60. The IGF-I antibody utilized was AFP4892898 anti-hIGF-I (A. F. Parlow, National Hormone and Peptide Program, Torrance, CA). The intra- and interassay CV were 12.8 and 13.1%, respectively. Circulating concentrations of leptin were determined using the method described by Delavaud et al. (2000). Detailed descriptions of assay development including antibody production, are described in that publication. The intra- and interassay CV were 6.3 and 9.9%, respectively.
Statistical Analysis
Effects of lasalocid on return to estrus, postpartum weight change, BCS, P4, IGF-I, and leptin were analyzed by ANOVA and the GLM procedures of SAS (SAS Inst., Inc., Cary, NC), with cow as the experimental unit. The statistical model included treatment as the main effect. In the case of repeated measurements, treatment, cow within treatment, time, and the treatment x time interaction were analyzed as main effects, using cow within treatment as the error term. Differences between groups were determined using the PDIFF option of SAS with least squares means ± standard error reported for all variables. Least squares means for metabolic hormones and reproductive performance were calculated for each cow during the prepartum period, at calving, and during the postpartum period. The values were then used to test for correlations between metabolic hormones and reproductive performance. Concentrations of the circulating hormones P4, IGF-I, and leptin were correlated with BCS, BW, and PPI of the cows using the PROC CORR option of SAS. Chi squared procedures were used to compare first-service conception rate, percentage of cows returning to estrus, and pregnancy rates within 90 d postcalving. Time of conception relative to calving was evaluated using the Kaplan-Meier survival analysis estimate of SAS. Potential differences between treatments were evaluated using the Mantel-Cox logrank test in SAS.
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Results and Discussion |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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). During the prepartum period, L cows gained 1.2 kg/d compared with C cows, which gained 0.39 kg/d. This is in agreement with some previous research in which pregnant cows fed harvested forage and supplemented with an ionophore had increased ADG compared with pregnant cows that did not receive an ionophore (Hixon et al., 1982a; Grings and Males, 1985); however, it has also been reported that the ADG of pregnant cows was not increased by ionophore consumption (Clanton et al., 1981; Goehring et al., 1989).
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). During the postpartum period, there were no treatment differences (P > 0.10) in cow BW or BCS; however, there was a numerical advantage (P < 0.11) for increased cow ADG from calving to d 56 in L vs. C cows (0.49 kg/d vs. 0.30 kg/d, respectively; Table 1). Previous research has not demonstrated improved ADG for postpartum Bos taurus and Bos indicus cows consuming an ionophore (Jacques et al., 1986; Del Vecchio et al., 1988; Webb et al., 2001); however, Webb et al. (2001) reported negative ADG from calving to weaning in two dietary treatments that did not contain lasalocid, and positive ADG in two dietary treatments containing lasalocid. To further support the trend for increased ADG from calving to d 56, during the same time period, there was a treatment effect (P < 0.05) on BCSCG, with L cows improving in BCS by 0.30 and C cows decreasing in BCS by -0.06 (Table 1).
At weaning, there were no treatment differences in cow BW (P > 0.61), cow BCS (P > 0.26), or cow ADG from calving to weaning (P > 0.18; Table 1). There was a numerical advantage (P < 0.12) in BCSCG from calving to weaning, with L cows losing fewer units in BCS (0.34) compared to C cows, which lost 0.79 unit (Table 1). Again, the lack of significant treatment effects due to lasaloicd ingestion is in agreement with previous research in the postpartum cow (Jacques et al., 1986; Del Vecchio et al., 1988; Webb et al., 2001).
The results of this study provide evidence that provision of an ionophore prior to calving does increase prepartum ADG and has a tendency to increase ADG from calving to d 56 after calving. In a review by Sprott et al. (1988), it was suggested that using ionophores in low-quality forage diets may decrease intake and improve feed efficiency, but that supplementation of animals consuming a higher-quality diet ad libitum might increase rate of body weight gain. This would be in agreement with the results from this trial where the cows were maintained on high-quality winter pasture in which forage availability was not limiting and the cows were additionally supplemented with a high-energy concentrate mix.
Calf Performance
As designed, there was no difference (P > 0.72) in calving date between treatments, with an average calving date of March 6 and March 7, 2001 for C and L cows, respectively. Sex ratio was not different (P > 0.26) between treatments, with C cows having 7 males and 13 females, and L cows having 11 males and 10 females.
There was no treatment difference (P > 0.44) in calf BW at calving (36.2 vs. 37.8 ± 1.1 kg for C and L cows, respectively), at d 28 of age (63.8 ± 2.1 vs. 66.1 ± 2.4 kg for C and L cows, respectively), at d 56 of age (94.6 ± 2.6 vs. 93.1 ± 2.9 for C and L cows, respectively), or at weaning (245.4 ± 5.9 vs. 240.7 ± 6.0 for C and L cows, respectively). Calf ADG throughout the trial (1.04 vs. 0.97 ± 0.04 kg/d for C and L cows, respectively) and at weaning (0.90 vs. 0.88 ± 0.02 kg/d for C and L cows, respectively) were unaffected by treatment (P > 0.19). Additionally, there was no treatment difference (P > 0.79) in calf 205-d adjusted weaning weight (221.6 vs. 219.7 ± 5.3 for C and L cows, respectively). An increase in calf birthweight for cows fed an ionophore prepartum has been previously reported (Clanton et al., 1981; Hixon et al., 1982b; Padilla-Ramirez, 1998); however, this was not observed in this study. The lasalocid in this study was provided for a shorter period of time precalving (20 vs. 28 d) compared with the study by Padilla-Ramirez (1998), which could be partially responsible for the discrepancy.
The effects of supplementing cows with an ionophore on calf growth are quite variable. Previous data have been reported in which there were no effects of ionophore supplementation to cows on calf growth (Clanton et al., 1981; Hixon et al., 1982b; Hopman and Weber, 1986), and positive effects of ionophore provision to cows on calf growth were also observed (Lemenager et al., 1978; Goehring et al., 1989). The results of this study agree with previous results on Brahman and Brahman-influenced cattle in which there was no improvement in calf performance due to lasalocid supplementation of cows (Del Vecchio et al., 1988; Webb et al., 2001).
There was no difference due to sex of calf for calf BW (P > 0.73) at calving, at d 28 postcalving (P > 0.89), at d 56 postcalving (P > 0.51), or at weaning (P > 0.19). Calf ADG throughout the trial was also unaffected (P > 0.10) by calf sex. This agrees with the results from Webb et al. (2001) where no effect of calf sex on calf performance was found; however, in this study, there tended (P < 0.10) to be an effect of sex of calf on the 205-d adjusted weaning weight, with female calves tending to weigh less than male calves at weaning (214.6 ± 5.10 vs. 226.6 ± 5.5, respectively).
Postpartum Interval to First Estrus with Functional Corpus Luteum and Rebreeding
Postpartum interval was unaffected by treatment (P > 0.10), with an average PPI of 59 and 55 d for C and L cows, respectively. This disagrees with reports that an improvement in PPI occurred when cows were supplemented with an ionophore after calving (Hardin and Randel, 1983; Mason and Randel, 1983; Webb et al., 2001), but it is in agreement with results from Del Vecchio et al. (1988). When supplementation with an ionophore began approximately 28 d prior to calving, there was also a significant decrease in PPI (Padilla-Ramirez, 1998). The average PPI for C cows in this study was similar to the average PPI for control cows in the studies of Padilla-Ramirez (1998); however, the L cows had longer PPI than the cows provided lasalocid pre- and/or postcalving in the Padilla-Ramirez (1998) study. Cows in this study were maintained on ryegrass pasture throughout the entire trial; however, in the study conducted by Padilla-Ramirez (1998), cows were maintained on Coastal bermudagrass hay prepartum and then placed on ryegrass pasture. The lower quality prepartum forage source may have allowed for a greater effect of the ionophore pre- and postcalving in the Padilla-Ramirez (1998) trial.
There was a tendency (P < 0.13) for the L cows to exhibit more abnormal estrous cycles than the C cows (47.6 vs. 25%, respectively). Included as abnormal cycles were short cycles (<17 d), estrus without CL formation, and CL formation without estrus. These results are in agreement with the results of Webb et al. (2001) where approximately 35.3% of lasalocid supplemented cows exhibited short cycles compared with to 17.6% of control cows. These results indicate some level of increased reproductive activity prior to the resumption of normal cycles in the L vs. C cows. This activity may prime the hypothalamic pituitary axis to reinitiate the secretion of gonadotropins; however, the authors have no way of supporting this hypothesis with data from this study. In future studies with lasalocid, the frequency of abnormal cycles and their implications for cow performance should be considered.
Although there was no difference in PPI, a greater percentage (P < 0.05) of L cows conceived by 90 d after calving (43% of L vs. 15% of C). From d 80 to 105, a numerically greater number of L cows conceived compared with C cows (Figure 1). There was a tendency (P < 0.12) for this increase to be significant as evaluated by the Mantel-Cox test. This may have been due to a tendency (P < 0.08) for greater first-service conception rate in L vs. C cows (68 vs. 40%). Overall pregnancy rate at the end of the breeding season was numerically greater (P < 0.12) in L vs. C cows (86 vs. 65%).
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Endocrine Profiles
During the prepartum period and at calving, there were no treatment differences (P > 0.10) in circulating concentrations of P4, IGF-I, or leptin, nor were there significant treatment x time interactions for those hormones (Table 2). For the first 30 d postcalving and from calving until first estrus, there were no treatment differences (P > 0.10) in circulating concentrations of leptin or IGF-I (Table 2). There were no treatment differences (P > 0.86) in serum concentrations of P4 on d 6, 7, or 8 of CL formation (3.55, 4.27, and 4.95 ± 0.42 ng/mL and 2.34, 3.17, and 3.51 ± 0.37 ng/mL for C and L cows on d 6, 7, and 8, respectively). From calving until d 30, L cows tended (P < 0.06) to have higher circulating concentrations of P4 than C cows (Table 2). This tendency was perhaps maintained numerically (P < 0.14) until the first estrus (Table 2). Again, there were no significant (P > 0.10) treatment x time interactions influencing P4, IGF-I, or leptin for these periods.
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There have not been many reports of the effects of an ionophore on serum concentrations of IGF-I or leptin. In sheep, monensin has been reported to increase circulating concentrations of IGF-I at the periovulatory stage (Peclaris et al., 1999). In male goats, Strauch et al. (2001) found no additional benefit of monensin supplementation over that of energy supplementation for circulating concentrations of IGF-I; however, there was increased expression of IGF-I messenger RNA in the liver due to monensin supplementation. The results of this study do not indicate an effect of lasalocid supplementation on circulating concentrations of IGF-I.
Similar to IGF-I, few reports exist as to the effects of an ionophore on circulating concentrations of leptin. When rat adipocytes were cultured with monensin, it was found that the rate of leptin synthesis remained unchanged; however, the release of leptin mediated by insulin, glucose, and pyruvate was blocked (Levy and Stevens, 2001). In cell cultures where epididymal adipose cells of male Zucker rats were utilized, secretion of leptin was inhibited by addition of monensin to the cell culture (Turban et al., 2001). Leptin is significantly correlated with increased fat mass in women (Kohrt et al., 1996), and increases in weight have been shown to induce increased circulating leptin concentrations (Kolaczynski et al., 1996). It was hypothesized then that provision of an ionophore, which has been demonstrated to improve cow ADG, might increase leptin synthesis; however, the ionophore has negative effects on leptin secretion in vitro (Levy and Stevens, 2001; Turban et al., 2001). Therefore, if cows in the L treatment had increased leptin synthesis, the leptin may have not been released into circulation.
Due to the variable range in PPI (30 to 132 d), and in an attempt to discern differences between cows with variable PPI, cows were grouped by PPI into short (n = 8; 30 to 37 d) and long (n = 8; 78 to 132 d) groups. There was an equivalent distribution of C and L cows in each group. There was no group difference (P > 0.10) during the prepartum period in circulating concentrations of P4, leptin, or IGF-I, nor was there a group x time interaction (Table 3). At calving, there was also no difference between groups in these hormones (P > 0.10; Table 3). During the postcalving period, there was no significant (P > 0.10) group effect on P4 or IGF-I (Table 3); however, there tended to be a group x time interaction (P < 0.10) influencing circulating concentrations of leptin, with short-PPI cows having higher concentrations of leptin for the first 42 d postcalving (Figure 2). This suggests that leptin may have an effect on PPI.
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Correlations Between Metabolic Hormones and Reproductive Performance
Prior to calving, with all cows included in the analysis, there were significant negative correlations between leptin and P4 (P < 0.0001; r = -0.36) and IGF-I and P4 (P < 0.01; r = -0.20; Table 4). At calving, leptin was positively correlated with IGF-I (P < 0.04; r = 0.320), BCS (P < 0.06; r = 0.29), and cow BW (P < 0.02; r = 0.36), and was negatively correlated with PPI (P < 0.06; r = -0.29; Table 4). At this time, P4 was positively correlated with IGF-I (P < 0.03; r = 0.34) and BCS (P < 0.003; r = 0.45; Table 4). During the postpartum period, there was a negative correlation between leptin and PPI (P < 0.0001; r = -0.27), and positive correlations between leptin and cow BW (P < 0.02; r = 0.36) and leptin and cow BCS (P < 0.06; r = 0.29; Table 4).
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The significant positive correlations between leptin and IGF-I, BCS, and BW at calving, as well as between leptin and BW and BCS during the postpartum period, agree with both leptin and IGF-I being increased during a state of positive nutrition as opposed to a state of undernourishment. Finally, the significant negative correlation between leptin and PPI suggests that leptin is potentially involved in postpartum reproductive performance.
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Implications |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Footnotes |
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2 Present address: Animal Physiology Research Unit, ARS, USDA, S-107 Animal Sciences Research Center, Columbia, MO 65211.
3 Present address: Animal Science Dept., Tarleton State University, Stephenville, TX 76402.
Received for publication October 16, 2002. Accepted for publication February 10, 2003.
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Literature Cited |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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and follicular patterns in Brahman cows. Ph.D. Diss., Texas A&M University, College Station.
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